This invention has as an object a device for avoiding secondary impacts of a mass against a target-member, resulting from the bounces of the mass after the first impact.
More particularly, the invention concerns a device for avoiding secondary impacts of a mass secured at one end of a rigid arm pivotable about a support member, against a target member, which it strikes at the end of its fall.
Such a device may be advantageously provided on an apparatus for generating acoustic shear waves in the earth for seismic prospecting of the sub-soil and, particularly, on the device described in the French patent No. 2 276 599. This device comprises a target member provided with a ground coupling surface, at least one mass for striking the target-member and means for imparting to the mass a velocity having a component parallel to the coupling surface, said means comprising, for example, an orientable rigid support member, a rigid arm supporting the mass at its end, and driving means for lifting the mass by pivotation of the rigid arm with respect to the rigid support member.
The first impact is generally followed with one or more secondary impacts due to bounces of the mass against the target-member. The secondary impacts are generally of much lower amplitude than the first one, but they nevertheless generate secondary pulses whose echoes on the reflecting layers of the sub-soil disturb the seismic recordings of the echoes of the main pulse.